Charging,?.

[David Stepney]

David.

If the warning lamp goes very bright on the Winter setting, that suggests that the dynamo is trying to charge the battery through the warning lamp. I would suspect that the cutout is not working.

[David.H]

The difference between Summer and Winter charge: in "Winter" switch position, the two dynamo terminals are connected together, so the Field (smaller wire) gets lots of supply and so makes more electricity.

In "Summer", the supply to the Field goes through the field resistance which lowers the juice to the field and the dynamo makes less electricity and so isn't working too hard during the Summer.

This resistance, as standard, is a coil of rusty wire about 3/8" diameter and about 2 1/2" long, it usually lives under the control box, or sometimes in its own box on the dynamo.

It is also often broken.   If broken and the switching is working, you get full charge on "Winter" and none on "Summer"

I have read back, the field resistance has only been mentioned once.    And reading back reminded me that you had a problem with the ignition light - which has its own resistance in the form of a coil of thin wire wrapped around the holder.   Which I am not sure you got to the bottom of whether the assembly was the correct spec, or connected correctly.

Did you get the cut out to close when revving?

Have you checked the state of the field resistance and its connections?

Are you sure the warning light is correct in spec and connections - it almost sounds as if the field current is going through it - it isn't clear from your last what happens when, I think you have written "Summer" twice, when one of them should be "Winter".


For a simple system, it ties us all up in knots - don't get down, it will get sorted.


Easy solution to get mobile is just run on the battery - see a previous thread a week or two ago - and have another go at it later.   Gives you time to borrow cut-out, dynamo, switch, ignition light, as required, to swap over and nail the problem.

Slack Alice
The lamp resistance wire is not present. I have run a wire to D+ so the lamp works
I am using a 12v bulb (like on my other sevens)    I did fit a 6v 3.2 but that blew on winter charge, but gave a lovely light!
I don't know if the cut out is closing at high revs....I think not.
I do not have any resistance wire in evidence!
I have not been able (how?) to test the field resistance I have a digital meter....
Of course I can run without the dynamo,  but it grieves me that something doesn't work. If I have toreplace the cut out, so be it, but I don't want to spend money and find it wasn't thar after all!
I could try the cut out from the AD, but I would hate to fry it!
Thanks to all for your help etc!!
D

["Slack Alice" Simon]

If the cut out isn't closing (and everything else is correct) then charge isn't being switched to the battery, and the ammeter will not show a positive charge.

What happens to the ammeter reading if you close the cut out with the engine running at more than tickover?


I don't know where the field resistor is in the system with your kind of cut out - someone else will have to tell us.   I have the cutout with the bigger base, and the resistor is underneath, in the base.   You have to remove the cutout to get at it.   But yours ... I don't know.



You don't need a field resistor to get things working, but without it, the "Summer" position is meaningless. 

"Winter" means the two terminals from the dynamo are connected together and you should be getting full charge, which should go through ammeter to the battery if the points close and are clean enough to conduct electricity.

[John Cornforth]

Hi again David H.

The warning lamp brightness depends on the difference between battery volts and dynamo ouput volts.  When things are working properly, it will have (6 - 0) = 6 V when the dynamo is stationary and will therefore be fairly bright.  As the dynamo begins to turn slowly, it will have for example (6 - 3) = 3 V and will be dimmer.  When the dynamo turns faster it will have for example (6 - 6) = 0 V and will go out.  A bit faster still and it will have (6 - 7) = -1 V which may or may not be enough to see it start to glow again very dimly.  Any faster and the cutout will close at just over 7 V, beyond this point the battery voltage will be the same as the dynamo output as they are shorted together by the cutout contacts. So no more glow.

BUT, if the cutout doesn't close at 7V, the dynamo output will rise quickly as its speed rises, as it has no load.  So you could easily get (6 - 12) = -6V, then (6 - 14) = -8V etc etc. The bulb doesn't mind that the voltage is now the opposite way round to normal, it will still merrily glow and will get brighter and brighter as you rev up, especially on the winter setting.

So from the symptoms you describe, it would seem that the your cutout is faulty.  You have already measured the shunt coil resistance which appears to be ok, so some other effect must be preventing it from closing properly even at voltages way over 7V.  I am guessing that you don't have access to a variable voltage power supply to allow you to test it off the car (or at least disconnected) so you may be stuck with testing it by substitution. Any 6V Austin Seven cutout will do if you can borrow a known good one.  The terminals may be in a different order but I am sure you could figure out which goes where.

Hope this makes sense.   Cheers,  John.

[David.H]

Thank you John
Very helpful as usual!
I might risk swapping the AD cut out.
The niggle is that I have seen it charge! The unaccustomed activity has clearly frightened it!
David

[David.H]

Well....
I swapped the RF cut outs over yesterday.
The AG (not charging) one went on to that AD and did not work! Stupidly I only tried it on summer charge.
The good AD one put onto the AG made no difference. no charge, warning light as before.
Put them back, both worked as before.....But I remembered that on the AD the charge rate on Summer is minimal & healthy when on Winter....so would it have made a difference? Probably not.
Not much progress! Except that it seems to me that the RF on the AG is probably faulty: the RF3 on the AD is ok! and the dynamo on the AG may also be suspect.....unless anyone has other ideas!
D

[Reckless Rat]

David, have you tried moving the 3rd brush a bit in either direction? It may just be a tad out of sync.

[David.H]

Thanks, worth a try! ....er, which is the third brush & which way do I move it? 
D

[Reckless Rat]

It's the one with a sliding mount on the left hand side of the dynamo as you look at it end on. The other two brushes are diametrically opposed and their carbons are twice as thick, so it's the thin one that's the third brush. If I remember correctly, rotating the brush anticlockwise increases the output. There is no need to undo anything (except removing the dust cover if it's still there) the brush should slide with finger pressure. Give the commutator a clean while you're at it with a cloth.

[David.H]

Sent an hour or so (at a safe distance!) with a neighbour who understands electrics much better than I. He quickly established that the field wiring in the dynamo is not functioning as it should. He traced it back to the switchboard & suggested that the switch was not feeding to the Field terminal on the dynamo and that the resistance between Winter & Summer settings was also not working.
This does not mean, he suggested, that the cut out may not also be faulty, but his tests indicated it was probably ok (as had my readings), The dynamo may be functioning since (as he opined) even with residual power at Field in the dynamo , as it speeds up it will, and appears to, generate some volts.
I had previously taken the Switch board apart & cleaned & reassembled it & it appeared to be working, but something is amiss.
Who is the "go to" person for checking/sorting switchboards? The warning lamp could also have a better connection than the one I have jury rigged!